1. Amplitude Feedback Subcircuit Schematic Modifications
Level Shifter
Without level shifters, envelope detector output does not overlap with full input range of log amp. Level shifters increase correction range.
Reference
Feedback
Envelope Detectors
Error Calculator
Log Amps
Attenuator

2. Candidate Topologies for Level Shifters
Op-amp level shifter
Accurate and easily adjusted
Limited bandwidth due to wires splicing it onto PCB
AC coupling
Simple, easiest modification
Blocks low frequency components of signal
Diode level shifting circuit
Simple, easy modification
Some distortion due to voltage drop across diode
Tested each topology on breakout boards and on PCB
Diode level shifter performed best on system board

3. Phase Detector Output Signals for Single Tone Inputs
500 MHz
Distinct logic “hi” and “low” levels
Well defined square wave output
Accurate phase error measurements
2 GHz
Indeterminate logic “hi” and “low” levels
Not a well defined square wave output
Invalid phase error measurements

4. Phase Detector & Error Measurement Subcircuit Schematic
Prescaler
Vref
Phase Ref
Comparator
Phase FB
Attenuator
Phase Detector
Error Calculator
Phase Shifter
Phase Detector & Error Measurement Subcircuit Schematic
Proposed modifications:
Prescaler (frequency divider)
Reduce frequency by ½ or ¼
Tested successfully 1-tone
Comparator
Clean up inputs (fast rising edge)
Testing evaluation boards
Both subcircuits are “add-ons”

5. Candidate Prescalers & Dividers
On Semi Prescalers & Dividers*
Part #
Description
Propagation Delay (pS)
Rise & Fall Times
(pS)
MC12095
2.5 GHz prescaler,
 2 or  4
Not specified
NB7L32M
2.5V, CML,  2
200 30
MC10EP32
3.3V, ECL,  2
350
120
MC10EL33
5V, ECL,  4
650
225
* Initially limiting candidates to On Semi components to ensure compatibility w/ phase detector
Test Status: the MC12095 was tested successfully at 2.14 GHz

6. Circuits for Sharp Input Edges
Schmitt Trigger Inverters
Commercially available
SN74AUC1G04 VH = 1.2V, 0.8 nS propagation delay
NLX3G14 VH = 1V, 4 nS propagation delay
Non-Commercially available
VH=0.42V, 170 pS switching speed
Comparators
Analog Devices ADCMP573, propagation delay 150 pS
On Semi MC10E1651, propagation delay 775 pS
Linear Technology LTC5564, typical response time 7 nS

7. ADCMP572 Evaluation Board Measurement
Outputs
Input
f = 5 MHz
Typical rise and fall times for ADCMP57X are specified as 35 pS